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At least 1,621 records · Page 90Linked to original sources
PubMedDate not supplied

"A retrospective cohort study for prognostic significance of visual acuity for near over that for distance in anisometropic amblyopia.".

A cohort of 50 anisometropic amblyopes, between the ages of 2.5 to 10 years, was studied retrospectively to assess the prognostic significance of visual acuity for near over that for distance. There is ample evidence in the literature for a significantly lower accommodative response in the anisometropic amblyopic eye. It has been proposed that the efferent accommodative dysfunction may be a fundamental and causative factor in anisometropic amblyopia. A reduced visual acuity for near over that for distance was found in 17 [34%] patients and in 11 out of these the near vision improved after an addition of +3.0D sph. When a reduced visual acuity for near, was obtained it was difficult to determine whether the visual afferent system (due to insufficient visual input), or the accommodation efferent mechanism was responsible. However an improvement in corrected near vision by addition of +3.0D sph. suggested an accommodative dysfunction. In patients with reduced visual acuity for near over that for distance, not only was the final visual outcome poor but also the onset of visual improvement in response to amblyopia therapy was delayed.

Amblyopia↗
PubMed1992

Visual scene effects on the somatogravic illusion.

This study attempted to determine which visual scene cues are most effective in overcoming the somatogravic illusion (SGI), a form of spatial disorientation that occurs when a shift in the resultant gravitoinertial force vector created by a sustained linear acceleration is misinterpreted as a change in pitch or bank attitude. Nine subjects were exposed to a gravitoinertial force shift of -30 degrees in the pitch plane, both with their eyes closed and while viewing computer-generated visual scenes through a wide field-of-view head-mounted display. The scenes depicted acceleration over a shoreline by means of horizon, texture, perspective, and color cues that were presented both in isolation and in various combinations. None of the scenes significantly reduced the magnitude of the SGI relative to the eyes-closed (baseline) pitch illusion, even though the textured scenes produced some linear vection. It remains to be established whether low-cost head-mounted visual displays can reliably reduce the magnitude of the SGI and other spatially disorienting illusions.

Acceleration↗
PubMed1992

Influence of windshield tint and tilt on recognition distance under mesopic conditions.

The influence of the angle of inclination and tint of windshields on recognition distance was tested in 94 subjects aged 20-83 years. Both clear and tinted (heat-absorbing) windshields were tested. Light transmission (in the vertical position) was 90.3% for the clear windshield and 81.0% for the tinted windshield. The windshields could be set at angles of 0 degree (vertical), 30 degrees, 50 degrees and 70 degrees of inclination. The tests were performed at night with low-beam headlights (mesopic conditions). A Landolt ring (diameter 43.5 cm; contrast 1:1.5) served as a test stimulus; it was painted on a disc 87 cm in diameter that could be rotated in steps of 45 degrees. The mean recognition distance without the windshield was 32.2 m +/- 5.5 m (mean +/- SD). It decreased to 31.0 m +/- 5.6 m (29.0 m +/- 5.3 m) by using a clear windshield in the vertical position (values for the tinted windshield are shown in parentheses): 30.1 m +/- 5.6 m (27.9 m +/- 5.3 m) with a 50 degrees angle of tilt, and 28.5 m +/- 5.4 m (26.9 m +/- 5.1 m) with a 70 degrees angle. The differences between the recognition distances obtained using the various tilts and tints were small but statistically significant (P < 0.01 in all cases: Student's paired t-test). Since the performance of the human eye is stressed to its limits during nighttime driving, our study suggests that extreme tilt of the windshield should be avoided and that the option of delivering cars equipped with a heat-absorbing but clear front windshield should be provided.

Accidents, Traffic↗
PubMed1992

Nonvisual judgment of the crossability of path gaps.

The ability of persons to locomote without vision with the aid of a hand-held probe was investigated in 4 experiments focusing on the negotiation of gaps in a pathway. In Experiment 1, Ss of extreme heights judged under sighted and blindfolded conditions whether gaps of different sizes could be crossed by walking. Crossability boundaries were lower for shorter Ss, but the height effect disappeared under normalization by leg length. Experiments 2-4 altered mechanical aspects of the probe (length and mass distribution) in the nonvisual case. Ss' performance was still reliable in each experiment, and their performances were constrained by parameters of the gap and of their action systems. Probe variables, however, had surprisingly little influence on the judgments of crossability. Results were discussed in terms of potential roles for information in different perceptual modalities.

Adult↗
PubMedDate not supplied

Low vision rehabilitation: visual acuity measurement in the low vision range.

1. To predict function and prescribe low vision aids, accurate measurements are needed. The routine measurement range can be extended by moving test charts normally used at 20 ft to a closer distance; 1 m is recommended, which gains a factor of 6. 2. Some practitioners recommend testing all reading at a standard distance, but they differ in the distances they recommend. Using a variable distance and recording the distance with every measurement allows for patients' preferred distances. 3. If the distance and letter size are properly recorded, the same visual acuity score should be calculated for all distances. Inches and J numbers, the most prevalent measurements, make visual acuity calculations impossible, but by adopting metric measurements, calculations are far easier.

Distance Perception↗
PubMed1991

Errors in distance appreciation and binocular night vision.

Studying binocular vergence in relation to luminance levels, we isolated two types of behaviour which may explain differences in distance appreciation: 1. Underestimation of distances in subjects with overconvergence in darkness. 2. Overestimation of distances in subjects with underconvergence in darkness. Progression towards the limiting value of convergence varies from one individual to another for each mesopic and scotopic luminance level and for different experimental conditions: variable discrepancy between the observation distance and the tonic vergence distance; accommodative or fusional stimuli at varying degrees of eccentricity; mobile stimuli in the observer's peripheral field. The study of bipartition in depth of a given interval for different observation distances confirms the existence of two major categories of individuals. Over- or underestimation of the nearer subjective half correlates to the binocular dark convergence capacity of each individual. These findings may explain errors in distance appreciation for road users in night vision.

Convergence, Ocular↗
PubMed1991

The linearity of proximally induced accommodation and vergence.

This study sought to determine the linearity and amplitude of both proximally induced accommodation (PIA) and vergence (PIV) by comparing the open-loop accommodation and vergence responses, respectively, to individual stimuli located at viewing distances ranging from 0.20 m to 1,500 m. For the measurement of PIA, the vergence and accommodation loops were opened by subjects (N = 10) monocularly viewing the target through a 0.5-mm pinhole, while accommodation was assessed concurrently using an infrared optometer. In the assessment of PIV, the accommodation loop was opened either by subjects (N = 10) viewing a low-frequency difference of Gaussian (DOG) grating or by viewing the targets binocularly through 0.5-mm pinholes. For both PIV methods, the vergence loop was opened by vertical dissociating prisms while the heterophoria was assessed for the various target distances using the von Graefe technique. The results demonstrated significant changes in both PIA and PIV for stimuli located closer than 3 m. However, both proximal components attained a minimum level and remained constant for targets at or beyond 3 m. Furthermore, the magnitudes of PIA and PIV were linearly related to the target distance measured in diopters and meter angles, respectively. These findings clearly demonstrate the influence of target proximity on the oculomotor system.

Accommodation, Ocular↗
PubMed1991

Accommodative hysteresis. Fundamental asymmetry in decay rate after near and far focusing.

The resting level of accommodation, or dark focus (DF), was compared before and after subjects maintained 8-min of clear focus on targets either at the far point (FP) of accommodation or at an equivalent dioptric distance on the near side of the DF. Although both conditions showed significant shifts in tonic accommodation in the direction of their respective fixation targets, only after near fixation was the shift maintained in darkness for 24-min postfixation. After FP viewing the aftereffect decayed in darkness with a significant linear trend (P less than 0.05). Thus, maintaining focus on a near target is more likely to induce an enduring adaptive shift in tonic accommodation than is far-target viewing, for reasons associated with the systems controlling far and near accommodation, respectively. Additional analyses provided further evidence that the degree of separation of the target from the DF is a highly significant factor controlling individual differences in initial adaptation levels.

Accommodation, Ocular↗
PubMedDate not supplied

[Effect of destruction of the auditory centers of the brain on the range of echolocation by bats Rhinolophus ferrum-equinum (the large horseshoe-nose bat)].

Effect of the auditory cortex, internal geniculate bodies and inferior colliculus removal on echo-ranging detection of immovable wire obstacle by bats has been studied in the behavioural procedure. It is shown that destruction of the auditory cortex results in an irreversible decrease (to 74.6% of control values) in limiting detection range of obstacle by animals. Extensive destructions of internal geniculate bodies decrease limiting detection range only in the first postoperative days. In the case of the inferior colliculi + removal the limiting detection range irreversibly decreases to values equaling 38.5% of control ones. A suggestion that the obtained effects are a consequence of the auditory system sensitivity deterioration in bats is substantiated.

Animals↗
PubMed1990

[Height vertigo, fear of heights, acrophobia].

Height vertigo (acrophobia) is a very frequent phenomenon being of interest for its physiological and psychological background, though usually only of limited significance in neuropsychiatry and otology. The different aspects as to its nature and origin are discussed. If acrophobia has developed into a conditioned reaction of avoidance with pressure of suffering, or acrophobia in persons, who have to work at heights, behavior therapeutic measures with systematic desensibilisation, starting from an imaginative training, are indicated.

Altitude↗
PubMed1990

Effects of stimulus distance on measurements of dark convergence.

Dark convergence is often measured psychophysically by aligning two dichoptic stimuli, which are briefly flashed in a dark surround. In the present study, the effect of different stimulus parameters on dark convergence measurements was investigated. Chief among these was the effect of viewing distance (50, 100 and 500 cm) of the stimulus. Measured dark convergence was biased towards the actual viewing distance of the stimuli; this effect was stronger with bar stimuli than with point-and-line stimuli. Measured dark convergence depended on the viewing distance to a lesser extent if bar stimuli were observed through pin-holes (open accommodative feedback loop). The subject's knowledge of the viewing distance had a small but significant effect; the size of the nonius bars had none. To reduce artefacts due to the stimulus distance on psychophysical measurement of dark convergence, point-and-line stimuli should be used at a viewing distance of about 1 m. In this case, the effect of stimulus distance can be about 0.25 meter angle (ma), averaged over subjects, but it may be as large as 0.5 ms in some individuals.

Adolescent↗
PubMed1990

Proximal and cognitively-induced accommodation.

The aim of this study was to investigate proximally-induced accommodation (PIA) at two levels of cognitive demand. PIA was assessed by comparing the open-loop accommodative responses to stimuli located at viewing distances of 6 m (0.17 D) and 0.33 m (3 D), respectively. The vergence and accommodation loops were opened by subjects monocularly viewing the targets through a 0.5 mm pin-hole. PIA was measured while subjects either were encouraged to relax and listened to popular music, or performed a relatively demanding mental arithmetic task (counting backwards in sevens). The results indicated that for 4 of the 12 subjects examined, increased cognitive demand produced a marked (greater than +/- 1.00 D) change in the magnitude of PIA. This finding suggests the presence of an interaction between the output of proximally- and cognitively-induced accommodation in these subjects. Such an interaction may hinder attempts to examine individual, non-optical components of accommodation.

Accommodation, Ocular↗
PubMed1990

Misconceptions about motion: development and training effects.

2 experiments were performed to examine whether children and adults possess a single-object/single-motion intuition. This intuition involves the view that because all parts of a rigid object move together, they all must move at the same speed. We found that third graders, sixth graders, ninth graders, and adults all responded in accord with this intuition. On problems where the intuition led to errors, a large majority of subjects of all ages answered incorrectly. On problems where it led to successful performance, subjects answered more accurately than on problems where the intuition was not applicable. In addition, the specific errors were those that the intuition yielded, and the intuition fit individual patterns of performance. The intuition not only influenced speed judgments but also judgments of distance traveled. Experiment 2 demonstrated that making sixth graders aware of the intuition and providing them kinesthetic experience that contradicted it produced significant improvements in the children's understanding. Implications for how scientific misconceptions in general can be overcome were discussed.

Acceleration↗
PubMedDate not supplied

Effects of sighting and sensory dominance on monovision high and low contrast visual acuity.

We investigated the relationship between ocular dominance and monovision visual performance in 15 presbyopic subjects. Ocular dominance was determined using sighting (hole-in-the-card and mirror tests) and sensory (anisometropic blur suppression test) methods. Correcting the dominant sighting eye for a given viewing distance was found to be an unreliable method of optimizing blur suppression or binocular high/low contrast visual acuity at that distance. If there is any advantage to a particular strategy for selecting the distance monovision eye, it must be realized in vision performance areas other than visual acuity.

Adult↗
PubMed1990

Gestalts are more closely associated with performance on a discrimination task than are component stimuli.

Distance, similarity, and other components of the physical stimulus but also gestalts are associated with the ability to discriminate between two objects. The present research bears on this confound. Identical lines were added to the opening and closing bracket of a pair of brackets to form two identical rectangles. A stimulus consisted of either one or two of these brackets, lines, or rectangles. Subjects indicated as quickly as possible whether one or two objects occurred. The discriminations between two near brackets and two near lines were more difficult than the discrimination between two near rectangles. A large distance between two objects improved the bracket and line discriminations more than the rectangle discrimination. Single brackets and lines did not result in poorer performance than did single rectangles. These results disconfirm the distance, similarity (including relational similarity), good continuation, location of geometric centers, size, closedness, symmetry, spatial frequency, redundancy, and number of lines component stimulus predictions at least twice. Both the two near brackets and the two near lines produce single gestalts, whereas each remaining 2-object stimulus results in two gestalts. Therefore, gestalts predicted performance better than did component stimuli. Another result was that the 2-object responses were faster than the 1-object responses for far objects.

Analysis of Variance↗